REPORT OF THE SOCIETY 99 



2. Sprout tubers before planting and discard those with weakly sprouts, or 

 if apical sprouts are strong while basal sprouts are spindling cut off and discard 

 the stem-end. 



3. It is probable that dusting the cut surface with fineh' ground sulphur 

 would be helpful. 



(h) Black dot disease 



Ducomet in France, in 1908, reported the occurrence for the first time of a 

 disease which he called "dartrose" caused bj' Vermicularia varians. McAlpine 

 some two years later found it in Victoria, Australia, and Doidge more recently in 

 South Africa. McAlpine named it "Black dot disease", an excellent descrip- 

 tive name. 



In the late summer and autumn of 1921 I discovered what appears to be 

 the same disease at Macdonald College in Quebec. This is the first time its 

 appearance is noted on this continent and a full description will be given later 

 elsewhere. 



Symptoms 



The first symptom is a slight yellowing of the foliage which begins at the 

 tips of leaflets and gradually involves the whole leaves. It may or may not be 

 accompanied by dwarfing of the plant depending upon the earliness and severity 

 of the infection. The yellowing will show early in the season on plants heavily 

 infected but usually it is a midsummer symptom. The yellowing is followed by 

 browning and withering of the leaves and if moist conditions prevail minute 

 black sclerotia will develop on the surface. At this time the lower stem parts 

 are covered with sclerotia and gradually the stem darkens and becomes brittle. 

 On opening the stem the pith is seen to be disorganized and sclerotia line the 

 inside walls of the vascular cjdinder. Figure 11 indicates the size and number 

 of the sclerotia both on the inside and outside of the stem. Roots and rhizomes 

 are attacked and the tubers are covered with the minute sclerotia. It appa- 

 rently does not cause serious damage to the tuber since the mycelium is confined 

 to the superficial tissues and the sclerotia are developed on the surface or are 

 slightly erumpent. 



Mycelium is to be found throughout the stem and leaf tissues of yellowed 

 plants which have sclerotia on the leaves. 



The organism 



Ducomet describes the sclerotia as astomic pycnidia 75 — 150 microns in 

 diameter with setae 100 to 130 microns long and at least biseptate. The spores 

 are slightly curved and 18-22 microns bj' 2.5 to 3 microns. In my cultures the 

 spores are slightly smaller and the setae longer and no pycnidia have been found. 

 McAlpine also states that he has found no pycnidia in Australia. More detailed 

 discussion will appear elsewhere. 



